Multivariate approach to photocatalytic degradation of a cellulose bleaching effluent

TiO2-photocatalytic degradation of a cellulose ECF effluent was evaluated using multivariate experimental design. The effluent was characterised by general parameters such as AOX, TOC, COD, colour, total phenols, acute toxicity and by the analysis of chlorinated low molecular weight compounds using GC/MS. The pH, catalyst amount and hydrogen peroxide were simultaneously varied using multivariate analysis to establish the weight of each variable in the COD and AOX removal after 180 min of reaction. The pH has a large effect in the AOX degradation at values below 5 and over 10, while COD removal is improved at low pH. The presence of hydrogen peroxide in the photocatalytic reaction has a small effect in degrading the AOX and COD. The optimal concentration of TiO2 was found to be around 1 gl−1. In addition, the reaction was monitored for longer periods of irradiation by carrying out TOC, COD, AOX, acute toxicity and spectrophotometric analysis, concluding that the organic matter contained in the effluent was significantly degraded. After 30 min of reaction more than 60% of the toxicity was removed and after 420 min of reaction none of the initial chlorinated low molecular weight compounds were detected, suggesting an extensive mineralisation which was corroborated by 95 and 50% AOX and TOC removals, respectively. Colour and total phenols were also removed.